Nitrate in stable CAPD patients and during peritonitis

During continuous ambulatory peritoneal dialysis (CAPD) peritoneal vessels are dilated. Nitric oxide (NO) causes vasodilation in many organs. Nitrate, a stable metabolite of NO, was measured in plasma and dialysate. In 6 stable CAPD patients standard peritoneal analyses were performed. The mass transfer area coefficient (MTAC) of nitrate was 11.5 mL/min (10.0-17.0 mL/min) (median and range). The MTAC of creatinine was of the same order of magnitude: 10.7 mL/min (8.0-14.2 mL/min), although the molecular weight of nitrate is lower (62 vs 113 dalton). The correlation between the MTAC of nitrate and the MTAC of creatinine indicated diffusion from the circulation and not local production of NO (r = 0.71; p = 0.11). Peritoneal permeability is increased in the acute phase of peritonitis, partly caused by extensive vasodilation. The potential role of NO during peritonitis was investigated in 8 CAPD patients with 11 peritonitis episodes in the acute phase and after recovery. The median dialysate/plasma (D/P) ratio of nitrate in the acute phase was 1.47 (range 0.96-2.55), which was higher than after recovery: 1.07 (0.99-1.75), p < 0.05. No relation was found between the D/P ratio of nitrate and the D/P ratio of TNF alpha (tumor necrosis factor). In conclusion, dialysate nitrate levels in stable CAPD patients are likely to be determined by diffusion from the circulation. D/P ratios exceeding 1.0 during the acute phase of peritonitis are probably the result of local NO production. This may contribute to the marked vasodilation during peritonitis.